In the voltage multiplying circuit of the type involved in this application, a switching means cyclically connects a booster capacitor in parallel with an input voltage source for charging during a "charging" portion of an operating cycle, and during a "discharge" portion of the operating cycle the booster capacitor is switched into a series connection with the input voltage source across a storage capacitor. Since the potential across the booster capacitor cannot change instantaneously after switching, the booster capacitor serves as an additional voltage source during its serial connection with the input voltage source, thereby augmenting or "boosting" the potential applied to the storage capacitor. More particularly, charge is transferred from the booster capacitor to the storage capacitor thereby charging the storage capacitor to a predetermined voltage level which is ideally a multiple of the potential supplied by the input voltage source. Thereafter charge is cyclically transferred to the storage capacitor in the above manner to keep it charged to the predetermined voltage level. The storage capacitor continually supplies the multiplied potential to external circuitry and, therefore, its charge must be replenished in the above manner to make up for the current consumed by the external circuitry.
The switching means in such circuits commonly include charge and discharge switches which are responsive to respective charge and discharge control signals. More particularly, the charge switch connects the booster capacitor in parallel with the input voltage source in response to receiving the charge control signal, thereby charging the booster capacitor to a predetermined voltage. The discharge switch means receives the discharge control signal and connects the booster capacitor in series with the input voltage source across the storage capacitor, thereby transferring charge from the booster capacitor to the storage capacitor. In these prior systems it is possible for the charge and discharge signals to overlap, thereby simultaneously biasing the switches "on" for a period of time. If this occurs, spurious and undesirable discharge of the capacitors can result. Furthermore, if the switches are serially connected across the input voltage source, simultaneous operation of the switches can result in large current spikes and undesirable power losses.
A prior system which anticipates this problem is disclosed in U.S. Pat. No. 4,106,086 which issued Aug. 8, 1978 to Holbrook et al. In Holbrook et al. a circuit is disclosed which relies on a difference between transconductances of individual transistors to produce non-overlapping control signals. However, since the transconductance of a transistor determines its switching time, transistor manufacturers continually strive to increase the transconductance in an attempt to reduce the transistor switching times. Therefore, it is both costly and difficult to find commercially available transistors whose transconductances differ to the extent necessary to allow the Holbrook et al. circuit to function in the manner disclosed. It is possible to control the transconductances as required by Holbrook et al. if the circuit is manufactured using integrated circuit (IC) technology. However, integrated circuits are costly to develop and therefore uneconomical for low-production applications.
The present invention is directed to overcoming one or more of the problems as set forth above by providing a circuit for generating non-overlapping control signals which can be readily manufactured using commercially available components.